This invention relates to engine-driven welding power supplies and more particularly to a D.C. welding power supply using an engine-driven, multiphase alternator providing current to a multiphase thyristor rectifier circuit. The invention more particularly provides a method of supplying short circuit condition current from a multiphase alternator to a welding apparatus.
Self-contained gasoline or diesel fuel welding power supplies are popular products. Such products generally comprise a gasoline or diesel engine which drives an electrical generator having an electrical output which is used to create an arc and weld metal. Three-phase, alternating current generators are often used. One type of three-phase, alternating current generator is known as a three-phase, brushless induction alternator. Such alternators have advantages in that they are generally less expensive than other types to manufacture, are rugged and generally dependable. One shortcoming of brushless alternators is their behavior when their output is short circuited. Either no current flows or current flow is very erratic. In many applications, short circuit conditions are never encountered and the problem just described is not significant. However, in welding applications, short circuit conditions, or conditions very closely resembling a short circuit condition, are often encountered. A lack of output or erratic behavior during short circuit conditions are therefore significant problems.